Why Do Local Variables Require Finality in Lambdas, But Instance Variables Don\'t?

Local Variables Require Finality in Lambdas, Unlike Instance Variables

In the realm of lambdas, a peculiar dichotomy manifests itself: local variables necessitate the use of the final keyword, while instance variables do not. This distinction raises the question: why this stark contrast?

The answer lies in the fundamental divergence between local and instance variables. Local variables undergo duplication upon the creation of a lambda instance by the JVM. On the contrary, instance variables enjoy a more flexible existence, as modifications to them cascade to the encompassing class instance. Their scope permeates the entire outer class.

Visualizing closures, anonymous classes, and lambdas from the standpoint of variable scope offers clarity. Envision a copy constructor being invoked for each local variable passed into a closure. This vivid mental model elucidates the contrasting behavior surrounding local and instance variables in the enigmatic world of lambda expressions.

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